Many devices used in biomedical applications require that the bulk of the device have one property, while the surface of the device has another property. For example, contact lenses may have high oxygen permeability through the lens to maintain good corneal health. However, materials that exhibit exceptionally high oxygen permeability (e.g. polysiloxanes) are typically hydrophobic and will adhere to the eye. Thus, a contact lens generally has a core or bulk material that is highly oxygen permeable and hydrophobic, and a surface that has been treated or coated to increase hydrophilic properties, thereby allowing the lens to freely move on the eye without adhering excessive amounts of tear lipid and protein.
In order to modify the hydrophilic nature of a relatively hydrophobic contact lens material, a coating may be applied onto the surface of a contact lens using a number of technologies, including a plasma treatment process, a Langmuir-Blodgett deposition process, a controlled spin casting process, a chemisorption process, a vapor deposition and a layer-by-layer polymer adsorption process. The layer-by-layer polymer adsorption (LbL) process could be one useful process for increasing hydrophilic properties of contact lenses. The prior art teaches that an article having hydrophilic surfaces can be coated using a LbL process, where the article having hydrophilic surfaces is dipped in a polyelectrolyte solution (e.g., polycations such as polyallylamine or polyethyleneimine). However, the prior art teaches that, prior to dipping, the surfaces of the article are treated in order to create surfaces having an affinity for the polyelectrolyte.
It was unexpectedly discovered by some of us that a LbL process can be used in coating hydrophobic contact lenses in dry or wet state without any pretreatment (WO9935520). By dipping iteratively lenses in an alternating fashion to a polyanion (e.g., polyacrylic acid, PAA) solution and a polycation (polyallylamine hydrochloride, PAH) solution, a hydrophilic surface can be coated onto the lenses.
During a LbL process, each of a plurality of lenses is generally held in a lens carrying cage which comprises a male and female basket halves. Many of such cages can be affixed together to form trays of baskets. Such trays may then be placed side-by-side to allow hundreds or thousands of lenses being simultaneously processed with a coating solution. However, there are several problems associated with the LbL coating processes, which could affect the quality of coatings on lenses. One problem is the adhesion of lenses to baskets which hold them. Since lens-holding baskets and/or trays generally have hydrophobic surfaces, lenses have a tendency to adhere on the baskets due to hydrophobic-hydrophobic interactions. This can affect the uniformity and completeness of coatings on lenses. In addition, when bubbles are formed in a coating solution, they tends to adhere to baskets and/or trays. Under such circumstance, bubbles can prevent a LbL solution from reaching the surfaces of lenses and result in bubble-defect in the lens coating. Therefore, there is a great need for developing methods and systems for efficiently coating a uniform hydrophilic coat to contact lenses.
Furthermore, when an aqueous LbL coating process is employed to modify the hydrophilic nature of a relatively hydrophobic contact lens material, microorganisms may grow in an aqueous coating solution and produce toxins (exotoxins or endotoxins) that may lead to physiological irritation or mammalian cell death. Such bioburden problem may be prevented by using antibiotics. However, widely using of antibiotics would lead to the proliferation of antibiotics-resistant bacteria. Therefore, there is need for a LbL coating process having a minimized bioburden level.
An object of the invention is to provide a method and system for applying a uniform liquid coating to an ophthalmic lens or a mold used to produce the ophthalmic lens.
Another object of the invention is to provide a LbL coating process having a minimized bioburden level.